Assessment of subchannel flow mixing coefficients for wire-wrapped hexagonal fuel rod bundles

Abstract

Flow mixing between adjacent subchannels within a wire-wrapped hexagonal fuel rod bundle affects radial heat transfer and determines the maximum cladding temperature, which is a key parameter to ensure the fuel safety margin in a sodium-cooled fast reactor (SFR). In the ENERGY model, both the effective eddy diffusivity and the edge swirl velocity ratio are employed to characterize the subchannel flow mixing. The Korea Atomic Energy Research Institute conducted subchannel flow mixing tests on the 37-pin and 61-pin bundle assemblies. The test assemblies were fabricated by reflecting thermal–hydraulic similarities of the Prototype Gen-IV SFR candidate cores. The subchannel flow mixing experiment was conducted using a wire-mesh sensing system. The subchannel flow mixing coefficients are determined by the least-square method so that the difference between the SLTHEN code prediction and experimental data is minimized numerically. The results show good agreement with the previous correlations, especially with the Cheng-Todreas model.